Method for Calculating Availability for Line Power Systems

ABSTRACT

A method for calculating availability in line power systems composed of power circuit modules determines power circuit parameters associated with the power circuits, accepting input from central databases. The method calculates a required number of power circuits to complete the line power system, and calculates the total power to be delivered over the power system, based on a power calculator. The method calculates individual power circuit availabilities based on the power circuit compositions and external variables. The method then calculates an overall system availability based on the power circuit availabilities and other external variable inputs. The method may compare the calculated line power system availability with a target availability, revise the power circuit parameters, and recalculate the system availability to meet the target availability.

BACKGROUND

1. Technical Field

This invention relates to line power systems. In particular, thisinvention relates to calculating availability for line power systems.

2. Related Art

Digital subscriber line (DSL) technology may include the digitalencoding of information transmitted on a local loop, i.e., theconnection between a customer's premises (home, office, etc.) and atelecommunications provider's central office serving the customer'spremises. Many existing local loops in the United States and throughoutthe world use twisted pair copper loops, originally designed for analogservice, or plain old telephone service (POTS). With digital subscriberloop technology, high speed access to the Internet, advanced telephonyfunctions, and multimedia services may be possible over the twisted paircopper access network. Digital subscriber systems may provide data fromspeeds of 64 kb/second in both upstream and downstream directions toover 10 Mb/second in a single direction.

DSL providers may be required to establish availability specificationsfor customers. Availability may be defined as the percentage of timethat services are available, or the percentage of time that providerequipment is functioning. DSL providers often provide availabilitymeasures on the order of 5 “9's” (i.e., 0.99999 availability). Toachieve this level of availability, a DSL system designer may takemultiple considerations into account, such as loop circuit topology andthe effect of external environmental variables on system availability.Availability calculations may become difficult and time-consuming.Availability parameters for various similar designs must be computedindividually.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereferenced numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is a block diagram of a line power system.

FIG. 2 is a block diagram of an example line power system.

FIG. 3 is a block diagram of a second example line power system.

FIG. 4 is a flow diagram of a process to calculate availability of aline power system.

FIG. 5 is a plot of an example line power system availabilitycalculation for aerial and buried copper line pairs as a function ofloop length.

FIG. 6 is a plot of an example line power system availabilitycalculation for aerial and buried copper line pairs as a function ofloop length for a line power system having one feed circuit.

FIG. 7 is a plot of an example upstream converter availabilitycalculation.

FIG. 8 is a plot of an example downstream converter availabilitycalculation.

FIG. 9 is a plot of an example line power system availabilitycalculation for one complete circuit.

FIG. 10 is a plot of an availability calculation for a first exampleline power system.

FIG. 11 is plot of an availability calculation for a second example linepower system.

DETAILED DESCRIPTION

A method for calculating availability in line power systems composed ofpower circuit modules determines power circuit pals associated with thepower circuits, accepting input from a central database. The methodcalculates a required number of power circuits to complete the linepower system, and calculates a power factor to be delivered over thepower system, based on a power calculator. The method calculatesindividual power circuit availabilities based on the power circuitcompositions and external variables. The method then calculates anoverall system availability based on the power circuit availabilitiesand other external variable inputs. The method may compare thecalculated line power system availability with a target availability,revise the power circuit parameters, and recalculate the systemavailability to meet the target availability.

A method for calculating the availability in a line power systemcalculates the availability parameter for various central office-servingarea interface (CO-SAI) based Line power systems and SAI based localpower designs quickly and efficiently. Availability is defined as theproportion of time a system is available to work, or the proportion oftime that service is available. For complex line systems, theavailability calculation process may be difficult. The method may useprobability theory applied to the specific designs. The designs may begraphically compared immediately for the next level of improvement tothe design. Actual loop lengths, prevailing ambient temperature, gaugemix, loop type and remote terminal origination are all possible inputvariables into the method. The method uses data imported from otherdatabases to perform the computation. The method may utilize theavailability models of ADTRAN, ALCATEL and TYCO power components and mayadd more redundancy to each either at the line (pair) level or thecircuit level to calculate the resulting availability. The ALCATEL modelprovides the number of circuits and pairs per circuit based on the looplength and number of customers at the SAI to ensure the electric currentdoes not cause the copper wire to heat up above a specified temperature.The ADTRAN and TYCO power calculators provide similar outputs fordetermining the number of circuits and pairs to complete a line powersystem.

The copper pair availability may be derived, using a power calculatorfor calculating pairs and circuits required with wire gauge, plant type(aerial, buried, or underground), and loop length. The power calculatormay be based on an ALCATEL calculator, or may be based on the powercalculator described in U.S. patent application Ser. No. 11/229,563,“Method for Configuring Power Loops between Central Office andSubscriber Access Interface” filed Sep. 19, 2005, which is incorporatedherein by reference. The ALCATEL power calculator is an industrystandard calculator that determines the required number of loopsrequired to complete a given line power system, as well as providing acalculation of the total power delivered to the line power system for agiven number of circuits and lines per circuit. The power calculator mayoutput the number of copper pairs per circuit (feeder circuits) and thetotal number of copper pairs required. The number of circuits (feeders)is the quotient of these two volumes. The total pairs required, numberof circuits required and the number of pairs per circuit (feed) all maybe functions of loop length. The number of pairs and number per feedboth may increase monotonically with loop length. The total coppercircuit availability may decrease with loop length as more loops areadded. The number of circuits may not be monotonic and consequently,system availability may rise each time another pair per feed isrequired. The number of converters—both upstream and downstream—may falleach time an additional pair per loop is required, affecting theavailability accordingly. The circuit availability may monotonicallydecrease, but the system availability may not monotonically decrease,and may rise or flatten as numbers of pair points are added.

FIG. 1 illustrates a line power system 100 that may include a centralpower circuit source, or a central office (CO) 105, a remote powercircuit delivery node 120, such as a serving area interface (SAI), alocation that may receive line power from the CO such as a remoteterminal (RT), or a unit that may include an RT and a controlled spacesuch as a controlled environment vault (CEV), and at least oneinterconnecting circuit system 110, such as a number of twisted paircopper wires or other system modules. The CO 105 may provide outputs tothe line power system such as electrical power or telecommunicationsignals, or a combination of both. Examples of telecommunication signalsinclude standard plain-old-telephone service (POTS) and/or very high bitrate digital subscriber line (VDSL)/asymmetric digital subscriber line(ADSL) services. The SAI 120 may be a remote active or passive devicethat may require a source of power. The SAI 120 may be powered by acommercial power source such as an electricity grid utility source, orthe SAI 120 may be powered from the CO 105 with electricity deliveredover the interconnecting circuit system 110, such as through twistedpair copper wires. Examples of the interconnecting circuit system 110include F1 wire loops extending from the CO 105 to the SAI 120 in a VDSLline power delivery architecture. The CO 105 may include an alternatingcurrent (AC) central power source such as a primary or back-upgenerator, direct current (DC) back-up batteries, or the CO 105 mayreceive commercial electricity from the electricity grid, which may thenbe conditioned for delivery to the SAI 120 through the interconnectingcircuit system 110.

The system works with “M-1” circuit systems, where M is the number offeeds connecting the CO 105 and SAI 120, but fails when two or morecircuits fail simultaneously during the same time interval. This mayoccur when two or more circuits are “not available.” All F1 line pairsmay fail because of a cable cut, or destruction of all the circuitsystems. This special case may be modeled as a dependent event. Anotherdependent event may be the operating temperatures for components in thesame environment, like an SAI, CO or CEV. The increased failure ratesdecrease the availability of all components operating in the sameenvironment.

FIG. 2 illustrates another line power system 200 depicting theinterconnecting circuit system 110 with further detail. The line powersystem 200 may include a unit for converting data, power, or acombination thereof at the CO 105, such as an upstream converter 205, aunit at the CO 105 for protecting the interconnecting circuit system110, such as a CO protector and power block 210, a number of twistedpair copper wire lines 215, a unit at the SAI 120 side for protectingthe SAI 120, such as an SAI protector and power block 220, and a unit atthe SAI for down-converting power and/or data, such as an SAI downstreamconverter 225. The copper lines 215 may be arranged in a number ofconfigurations. The copper lines 215 may be configured so that there isone feeder arranged between the CO 105 and the SAI 120, where a feedermay be defined as an interconnecting circuit coupling the CO 105 and theSAI 120. A circuit may comprise one or more pairs of wires in a loop.Alternatively, there may be more than one feeder arranged between the CO105 and the SAI 120. Additional feeders provide back-up redundancy ifthere are failures in the interconnecting circuit systems 110. A feedermay comprise one or more twisted copper line pairs. The required numberof copper line pairs per feeder may be determined by a circuit powercalculator, such as an ALCATEL power calculator or the power calculatordescribed in U.S. patent application Ser. No. 11/229,563, “Method forConfiguring Power Loops between Central Office and Subscriber AccessInterface.” The feeder may have more than the minimum required number ofcopper line pairs determined by the power calculator. The additionalline pairs may provide additional line power system availability byrequiring two or more line pairs to fail for an interconnecting circuitsystem 110 to fail completely. Additional feeders also may provideadditional line power system availability by requiring more than twointerconnecting circuits 110 to fail for the entire circuit system 110to fail completely.

The components in FIG. 2 may be in series, so if one link or componentfails, then the circuit also may fail. If an alarm circuit (not shown)fails and the alarm fails to notify the emergency maintenance system(EMS) system about a down circuit, then the availability may be lowered.This continuity may be modeled into the probabilities.

FIG. 3 illustrates an example line power system 300 that includes a CO105, SAI 120, and an interconnecting circuit system 210. The CO 105 andthe SAI 120 are separated in this example 300 by a loop length L. Inthis system, the interconnecting circuit system 210 comprises two feedercircuits (211 and 212), and each feeder circuit (211 and 212) comprisesone copper pair line (213, 214, 215, and 216). The circuit system 210may further include upstream power protection fuses (221 and 222),downstream power protection fuses (223 and 224), upstream power blocks(231 and 232), and downstream power blocks (233 and 234). The powerblocks 233 and 234 may include fuse boxes or fuse circuits. In this linepower system 300, the CO 105 includes two urea converter modules (206and 207), which may provide power and/or digital subscriber linkservices to the line power system 300 and the SAI 120 through the feedcircuits (211 and 212). The SAI 120 includes two downstream convertermodules (208 and 209) which receive inputs from the feeder circuits (211and 212). The CO upstream converter modules (206 and 207) may be TycoCPS3200U modules, for example. The SAI downstream converter modules (208and 209) may be Tyco CPS2500D modules, for example. The SAI 120 maysupply a communications device 250, with power, digital subscriber linkservices, or a combination thereof. In this system, the SAI 120 suppliesthe communications device 250 with 54V power and VDSL service. Thecommunications device 250 may be an Alcatel 7330 device, for example.

FIG. 4 illustrates a process that calculates availability for a linepower system. The line power system includes power circuits whichdeliver power through the line power system. The power circuits also mayserve as modules or sub-units of the line power system when calculatingparameters related to the line power system. Examples of power circuitsin the line power system include the modules illustrated in FIGS. 1-3,including CO 105 modules, SAI 120 modules, interconnecting circuits 110,upstream converters 205, upstream power protector and power blocks 210,copper wire pairs 215, downstream power protector and power blocks 220,and downstream converters 225. The method determines, at act 401, anumber of power circuit parameters characterizing each of the powercircuits. The power circuit parameters may include the number and typeof components in the power circuits, the locations of the powercircuits, the loop length, wire type, wire gauge, and other dimensionsof the wires interconnecting the power circuits, wire, component, andcircuit properties such as resistance, impedance, inductance, andcapacitance values, manufacturer information, and performance and repairfigures of merit. The data may be input from a database comprisingrecords of these circuit parameters, at act 405. The circuit parametersmay be input from a predetermined database, such as an Automated Recordsand Engineering System (ARES), Loop Facilities Assignment and ControlSystem (LFACS), or Loop Engineering Information System (LEIS) database,or may be input dynamically in real-time. The LEIS database is adatabase of engineering data, part of which is loaded from the LFACSdatabase. It provides the engineers with daily planning, designoperations, utilization and inventory data. This is a Telcordiadeveloped system. The LFACS database maintains an inventory of OutsidePlant (OSP) facilities and their relationships with customer addresses.It assigns service orders, supports plant rearrangement and helps withrepair/maintenance. This is a Telcordia developed system. The looplengths may be related to the loop gauge, and may typically be of 24 or26 gauge copper wire.

The method calculates a required number of power circuits to completethe line power system, at act 410. The method also calculates a totalpower to be delivered over the line power system, at act 420. Therequired number of power circuits and the power to be delivered over theline power system are calculated from a circuit power calculator. Thecircuit power calculator may process the circuit parameters determinedat act 401 to calculate a minimum number of power circuits, such ascopper wire pairs, required to transmit a given power load through theline power system. In this system, the power calculator may comprise anALCATEL calculator or the power calculator described in U.S. patentapplication Ser. No. 11/229,563, “Method for Configuring Power Loopsbetween Central Office and Subscriber Access Interface” for calculatingpairs and circuits required with wire gauge, plant type (aerial, buried,or underground), and loop length. The power calculator may output thenumber of copper pairs per circuit (feeder) and total number of copperpairs required. The number of circuits (feeders) may be the quotient ofthese two values. The total pairs required, number of circuits requiredand the number of pairs per circuit (feeder) may be all functions ofloop length. The number of pairs and number per feeder both may increasemonotonically with loop length.

The method calculates a first power circuit availability measure and asecond power circuit availability measure based on the power circuitparameters determined at act 401 and a plurality of external variables,at act 430. The method may take into account all the failure modes andthe failure rates of the CO based DC-DC converters, the outside plantcable and the SAI based DC-DC converters. The method, at act 430, mayapply a thermal failure acceleration factor to arrive at the overallsystem downtime for the first power circuit, which may comprise a CO105. The same analysis is applied for the SAI based local power option120, where the commercial grid outages (from Power UtilitiesCommission/Illinois Commerce Commission (PUC/ICC) databases), rectifierand battery failure rates are used to calculate the downtime. In oneembodiment, a thermal acceleration factor (from national weatherdatabases, for example) is applied for the components in the SAI 120 forarriving at the overall power system downtime.

The external variables may comprise variables such as the locations ofremote power circuit modules, such as an SAI 120; environmentalvariables, such as the temperature of the power circuit systems, theambient air temperature external to the power circuit systems; ambientatmospheric readings such as barometric pressure, humidity, dew point,wind velocities, solar angle (which may include the latitude of thegeographical location of the circuits), ground albedo, and solarexposure readings; and failure and/or repair statistics, such as thefailure-in-time (FIT), mean-time-to-failure (MTTR), ormean-time-to-repair (MTTR) of a particular power circuit. The failureand/or repair statistics may include Weibull and exponentialdistributions as well as other statistical descriptions of the failureand/or repair rates. The MTTR may be a discretionary repair commitment.The shorter the MTTR is, the more repair employees may be required, andthe greater the cost of maintenance. Other external variables which mayaffect the performance of a line power system may also be incorporatedinto the model. The external variables may be input from a predetermineddatabase, at act 425, or may be input dynamically in real-time asreadings occur.

The method then calculates a line power system availability based on thefirst power circuit availability, the second power circuit availability,and a number of external variables, at act 440. For the line powersystem depicted in FIG. 3, with one extra feeder and the minimum numberof copper pair lines per feeder, the line power system availability maybe calculated from:

$\begin{matrix}{{Av\_ system} = {\begin{pmatrix}{{Av\_ circuit}^{M} + {M*{Av\_ circuit}^{M - 1}*}} \\\left( {1 - {Av\_ circuit}} \right)\end{pmatrix}*}} \\{{{Av\_ no}{\_ cable}{\_ cut}}}\end{matrix}$ where: $\begin{matrix}{{Av\_ circuit} = {{Av\_ Upstream}{\_ Converter}*}} \\{{{Av\_ Copper}{\_ Pairs}{\_ Per}{\_ Feed}*}} \\{{{Av\_ Downstream}{\_ Converter}}}\end{matrix}$ $\begin{matrix}{{{Av\_ Upstream}{\_ Converter}} = \frac{\frac{1}{M\; T\; T\; R}}{\frac{1}{M\; T\; T\; R} + {{failure}\mspace{14mu} {rate}\mspace{14mu} {upstream}}}} \\{= \frac{\mu_{USC}}{\mu_{USC} + \lambda_{USC}}}\end{matrix}$ $\begin{matrix}{{{Av\_ Downstream}{\_ Converter}} = \frac{\frac{1}{M\; T\; T\; R}}{\frac{1}{M\; T\; T\; R} + {{failure}\mspace{14mu} {rate}\mspace{14mu} {downstream}}}} \\{= \frac{\mu_{DSC}}{\mu_{DSC} + \lambda_{DSC}}}\end{matrix}$

Where Av_system is the line power system availability, Av_circuit is theavailability of a power circuit within the line power system,Av_Upstream_Converter and Av_Downstream_Converter are the availabilitymeasures for the upstream and downstream converters (205 and 225respectively), Av_Copper_Pairs_Per_Feed is the availability of a copperpair in a feeder circuit, Av_no_cable_cut is the probability(availability) of no disruption or destruction of the interconnectingcircuit between the CO 105 and SAI 120, μ_(USC) is the repair rate forthe upstream converter 205, and λ_(USC) is the failure rate (FITS) forthe upstream converter. μ_(DSC) is the repair rate for the downstreamconverter 225, λ_(DSC) is the failure rate (FITS) of the downstreamconverter and M is the number of feeder circuits between the CO 105 andSAI 120.

In some systems, one copper pair per feeder is provided, i.e., no extracopper pairs are provided in the circuit. In those systems, if onecopper pair fails, then the feeder circuit fails. This is incorporatedinto the method as:

Av_Copper_Pairs_Per_Feed=(Av_Copper_Pairs)^(Pairs) ^(—) ^(per) ^(—)^(feed)

If all circuits are available, then the system is available. The modelalso may imply that if one circuit fails (when M>1), then the system isstill available for service. Only when all M feed circuits fail will thesystem be unavailable. Alternatively, the method may calculate the linepower system availability using a different relation if there are twoextra feeders per system, using:

$\begin{matrix}{{Av\_ system} = {\begin{pmatrix}{{Av\_ circuit}^{M} + {M*{Av\_ circuit}^{M - 1}*}} \\{\left( {1 - {Av\_ circuit}} \right) + {M*\frac{M - 1}{2}*}} \\{{Av\_ circuit}^{M - 2}*\left( {1 - {Av\_ circuit}} \right)^{2}}\end{pmatrix}*}} \\{{{Av\_ no}{\_ cable}{\_ cut}}}\end{matrix}$

where the parameters have the same definitions as above. In othersystems, where one extra pair of copper wire is provided for a feedcircuit, the failure of two copper wire pairs may result in the failureof the feed circuit. In these systems, this failure mode is incorporatedinto the method as:

$\begin{matrix}{{{Av\_ Copper}{\_ Pairs}{\_ Per}{\_ Feed}} = {\left( {{Av\_ Copper}{\_ Pairs}} \right)^{{Pairs\_ per}{\_ feed}} +}} \\{{\left( {{Pairs\_ per}{\_ feed}} \right)*}} \\{{\left( {{Av\_ Copper}{\_ Pairs}} \right)^{{{Pairs\_ per}{\_ feed}} - 1}*}} \\{\left( {1 - {{Av\_ Copper}{\_ Pairs}}} \right)}\end{matrix}$

The method may compare a predetermined availability metric with thecalculated line power system availability, at act 450. The predeterminedavailability metric may comprise a value selected by the system designeras the minimum acceptable system availability, or a customer requiredavailability target. The predetermined availability metric may be set atrun-time, or may be selected in real-time as external variables change.If the calculated line power system availability is greater than thepredetermined availability metric, then the method terminates. If thecalculated line power system availability is less than the predeterminedavailability metric, then the method may determine a new number of powercircuit parameters, at act 460, and calculate a new line poweravailability according to the method described above.

FIG. 5 illustrates a plot of a resulting example line power systemavailability calculation for aerial and buried copper line pairs as afunction of loop length. The copper wire may be 26 gauge, with one pairper feeder used in the availability model. This example system assumesthe MTTR is equal to 25 hours. As can be seen in FIG. 5, the copper pairavailability falls monotonically as loop length increases. Theavailability shown for 26 gauge, aerial cable and an MTTR=25 is of theorder of high “three 9s” (between 0.9997 and 0.9998).

FIG. 6 illustrates a plot of a resulting example line power systemavailability calculation for aerial and buried copper line pairs as afunction of loop length for an example line power system having only onefeeder circuit. This example assumes the MTTR is equal to 25 hours andthere are no allowable pair failures per feeder. As can be seen in FIG.6, the copper pair availability falls monotonically as loop lengthincreases, but the function steps down with the pairs per feeder jump ofthe power calculator determined model. Also, the availability shown for26 gauge, aerial cable and an MTTR=25 is in the “three 9s” order(between 0.9991 and 0.9998).

FIG. 7 illustrates a plot of a resulting example upstream converteravailability calculation for aerial copper line pairs of 26 gauge. Thisexample assumes the MTTR is equal to 25 hours. The three plot linesrepresent the operating temperatures plus ambient temperatures. The mostavailable function represents 104 F. The middle line representsavailability at 131 F, and bottom line represents availability at 158 F.As can be seen in FIG. 7, individual upstream converter availability maynot be a function of loop length, but the number of converters requiredis. Also, the availability shown for MTTR=25 is less than high “Four 9s”to nearly “Five 9s” (i.e., between 0.99989 and 0.99997).

FIG. 8 illustrates a plot of a resulting example downstream converteravailability calculation for buried copper line pairs of 26 gauge. Thisexample assumes the MTTR is equal to 25 hours. The three plot linesrepresent the operating temperatures plus ambient temperatures. The mostavailable function line represents 104 F. The middle line representsavailability at 131 F, and bottom line represents the availability at158 F. As can be seen in FIG. 8, an individual downstream converter'savailability may not be a function of loop length, but the number ofconverters required is. Also, the availability shown for MTTR=25 is lessthan low “four 9s” to nearly “five 9s” (i.e., between 0.9999 and0.99998). For pairs of 26 gauge, aerial and buried, the downstreamconverter circuit component availability is above the “five 9s” forMTTR=5 hours and temperatures less than 131 F. This may imply extremetemperature environments may stiff allow system availability above theoverall availability target. For pairs of 26 gauge copper line pairs,aerial and buried, the downstream converter circuit componentavailability is above the “five 9s” for MTTR=10 and 15 hours andtemperatures less than 131 F. This may imply moderate summer temperatureenvironments may still allow system availability above the overallavailability targets.

FIG. 9 illustrates a plot of a resulting example line power systemavailability calculation for one complete circuit for buried, 26 gaugecopper line pairs. This example assumes the MTTR is equal to 25 hours.The three plot lines represent the operating plus ambient temperatures.The most available function line represents 104 F. The middle linerepresents availability at 131 F, and the bottom line represents theavailability at 158 F. As can be seen from FIG. 9, the circuitavailability falls monotonically with loop length, but the functionsteps down as pairs per feeder are added based on the ALCATEL calculatormodel. Also, the availability shown for 26 gauge, aerial cable andMTTR=25 is from “three 9s” to high “three 9s” (0.999 to 0.9997). Looplength may affect circuit availability more greatly than doestemperature in this configuration.

FIG. 10 illustrates a plot of a resulting example line power systemavailability calculation for buried, 26 gauge copper line pairs with nopair per feeder allowed to fail without the circuit failing. Thisexample assumes the MTTR is equal to 20 hours. The three plot linesrepresent the operating temperatures plus ambient temperatures. The mostavailable function line represents 104 F. The middle line representsavailability at 131 F, and the bottom line represents availability at158 F. As can be seen from FIG. 10, the circuit availability fallsmonotonically as loop length is increased, but the function veryslightly steps down as pairs per feed are added based on the powercalculator model. The availability shown for 26 gauge, aerial cable andMTTR=25 is of the order of high “three 9s” to greater than “five 9s”(0.9998 to 0.999995). Loop length may have a greater effect onavailability than temperature does. The line power system availabilityis above “five 9s” level only for loop length˜7 kft and less than 131 For 4 kft and temperatures less than 158 F. Otherwise, the availabilityis less than “five 9s.”

FIG. 11 illustrates a plot of a resulting example line power systemavailability calculation for buried, 26 gauge copper line pairs with onepair per feeder allowed to fail without the circuit failing and twocircuits failing without the system failing. This example assumes theMTTR is equal to 20 hours. The three plot lines represent the operatingtemperatures plus ambient temperatures. The most available function linerepresents 104 F. The middle line represents availability at 131 F, andthe bottom line represents the availability at 158 F. As can be seenfrom FIG. 11, the circuit availability may not fall monotonically withloop length, but the function steps down and up as the number ofcircuits is modified based on the power calculator model. Theavailability shown for 26 gauge, aerial cable and MTTR=20 is of theorder of high “five 9s” (0.999997 to 0.999998). The temperature may havea greater effect on availability than does loop length. The systemavailability is above the “five 9s” level even with the MTTR=20 hoursfor all but the most extreme temperature (158 F) and the longest looplengths shown (>24 kft).

Calculations from the model in the application may imply that loop laffects line power availability more than does temperature difference,within the scale range of both variables in the current design, but withone more pair per feeder added and allowed to fail. Then theavailability increases greatly. Using the ALCATEL calculator, copperpairs per circuit (ranging from 1 to 7 pairs) have availability rangesfrom 0.9998 at 1 kft to 0.9992 at 24 kft (assuming MTTR=25). Theavailability of a single copper loop is less than “five 9s” even at theshortest loop lengths. Adding one additional pair per feeder to theALCATEL calculator, copper loops combined (1 to 7) pairs per circuithave availability ranges from 0.99999998 at 1 kft to 0.99999952 at 24kft (assuming MTTR=25). For one circuit, the upstream converteravailability ranges from mid “five 9s” at 5 hours MTTR and 104 F to high“three 9s” at 25 hours MTTR and 158 F. For one circuit, the upstreamconverter availability ranges from mid “five 9s” at 5 hours MTTR and 104F to “four 9s” at 25 hours MTTR and 158 F.

Using the ALCATEL calculator to determine the number of pairs per feederfor both upstream and downstream converters, the single circuitavailability ranges from high “three 9s” at 1 kft and 104 F to “three9s” at 24 kft and 158 F. These figures assume an MTTR=20 hours and 26gauge, buried copper pair lines. Adding one additional pair per feed tothe ALCATEL calculator—determined number of pairs per feeder for boththe upstream and downstream converters creates circuit availabilityranges from mid “five 9s” at 1 kft and 104 F to high “three 9s” at 24kft and 158 F. These figures assume an MTTR=20 hours and 26 gauge,buried copper pair lines. The availability differences are due totemperature and not loop length effects.

In some systems, the upstream converter may be located in a CO 105, CEV,or hut, but not in an RT. For the line power system as a whole, usingthe power calculator-calculated number of pairs per feeder for both theupstream and downstream converters, the single feed circuit availabilityranges from mid “five 9s” at 1 kft and 104 F to high “three 9s” at 24kft and 158 F. These figures assume an MTTR=20 hours and 26 gauge,buried copper line pairs. In systems where the upstream converter islocated in an RT, the availability decreases in the 5^(th) and 6^(th)decimal places.

Adding one additional pair per feeder to the power calculator-calculatednumber of pairs per feeder for both the upstream and downstreamconverters may result in availability ranges from mid “six 9s” at 1 kftand 104 F (with MTTR=5 hours ) to mid “five 9s” at 24 kft and 158 F(with MTTR=25 hours). The availability differences are due totemperature and not loop length effects. In systems where the upstreamconverter is placed in an RT, the availability decreases in the 5^(th)and 6^(th) decimal places.

In some systems, adding one additional circuit to the powercalculator-calculated number of required circuits may provide line powersystem availability from mid “six 9s” (0.9999995) at 1 kft and 104 F(with MTTR=5 hours) to high “five 9s” (0.9999963) at 24 kft and 158 F(with MTTR=25 hours). The availability differences are due totemperature and not loop length effects. In systems where the upstreamconverter is placed in RT, the availability may change in the 7^(th)decimal place.

In some systems, adding one additional circuit to the powercalculator-determined results and an additional pair per feeder(resulting in two extra circuits per system) may provide availabilityranges from mid “six 9s” (0.9999995) at 1 kft and 104 F (with MTTR=5hours) to high “five 9s” (0.9999963) at 24 kft and 158 F (with MTTR=25hours). The availability differences are due to temperature and not looplength effects. For systems in which the upstream converter is placed inan RT, the availability changes in the 7^(th) decimal place.

Like the method shown in FIG. 4, the sequence diagrams may be encoded ina signal bearing medium, a computer readable medium such as a memory,programmed within a device such as one or more integrated circuits, orprocessed by a controller or a computer. If the methods are performed bysoftware, the software may reside in a memory resident to or interfacedto a processor, a communication interface, or any other type ofnon-volatile or volatile memory interfaced or resident to the processor.The memory may include an ordered listing of executable instructions forimplementing logical functions. A logical function may be implementedthrough digital circuitry, through source code, through analogcircuitry, or through an analog source such as through an analogelectrical audio, or video signal. The software may be embodied in anycomputer-readable or signal-bearing medium, for use by, or in connectionwith an instruction executable system, apparatus, or device. Such asystem may include a computer-based system, a processor-containingsystem, or another system that may selectively fetch instructions froman instruction executable system, apparatus, or device that may alsoexecute instructions.

A “computer-readable medium,” “machine-readable medium,”“propagated-signal” medium, and/or “signal-bearing medium” may compriseany logic or software that contains, stores, communicates, propagates,or transports software for use by or in connection with an instructionexecutable system, apparatus, or device. The machine readable medium mayselectively be, but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. A non-exhaustive list of examples of amachine-readable medium would include: an electrical connection“electronic” having one or more wires, a portable magnetic or opticaldisk, a volatile memory such as a Random Access Memory “RAM”(electronic), a Read-Only Memory “ROM” (electronic), an ErasableProgrammable Read-Only Memory (EPROM or Flash memory) (electronic), oran optical fiber (optical). A machine-readable medium may also include atangible medium upon which software is printed, as the software may beelectronically stored as an image or in another format (e.g., through anoptical scan), then compiled, and/or interpreted or otherwise processed.The processed medium may then be stored in a computer and/or machinememory.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. Accordingly, the invention is not to be restricted except inlight of the attached claims and their equivalents.

1. A method for calculating availability for a line power system, theline power system comprising power circuits, further comprising:determining a plurality of power circuit parameters characterizing eachof the power circuits; calculating a required number of power circuitsto complete the line power system; calculating a total power deliveredto be delivered over the line power system; calculating a first powercircuit availability measure and a second power circuit availabilitymeasure based on the power circuit parameters and a plurality ofexternal variables; and calculating a line power system availabilitybased on the first power circuit availability, the second power circuitavailability, and the plurality of external variables.
 2. The method ofclaim 1 further comprising: comparing a predetermined availabilitymetric with the line power system availability; determining a newplurality of power circuit parameters if the line power systemavailability is less than the predetermined availability metric; andcalculating a new line power availability according to the method ofclaim
 1. 3. The method of claim 1 where the external parameters comprisea plurality of environmental variables.
 4. The method of claim 3 wherethe environmental variables are selected from the group comprising:ambient temperature, ambient humidity, wind velocities, latitude, andsunlight exposure.
 5. The method of claim 1 where the plurality of inputparameters is selected from the group comprising: a power circuit looplength, a number of central location circuits, and a number of remotecircuit locations, and the number of wire pairs per circuit.
 6. Themethod of claim 1 where the first power circuit comprises a centraloffice (CO) power converter.
 7. The method of claim 6 where the secondpower circuit comprises a serving area interface (SAI) power converter.8. The method of claim 5 where the power circuit loop length, the numberof central location circuits, and/or the number of remote circuitlocations are determined from a central database comprising a pluralityof parameters associated with the line power system.
 9. The method ofclaim 8 where the central database comprises a database selected fromthe group consisting of an Automated Records and Engineering System(ARES), Loop Facilities Assignment and Control System (LFACS), or LoopEngineering Information System (LEIS) database.
 10. The method of claim1 where the line power system comprises a very high bit rate digitalsubscriber line (VDSL) system or asymmetric digital subscriber line(ADSL) system.
 11. The method of claim 1 where the power circuitscomprise feeder circuits connecting the central office (CO) and theserving area interface (SAI).
 12. The method of claim 11 where thefeeder circuits comprise one or more copper line pairs.
 13. A method forcalculating availability for a line power system, the line power systemcomprising at least one power circuit unit interconnecting a centraloffice (CO) location and a serving area interface (SAI) location,further comprising: determining a loop length required for the linepower system; determining a number of CO location circuits required inthe line power system; determining a number of SAI location circuitsrequired for the line power system; calculating a required number ofline power system circuits based on the required loop length, therequired number of CO location circuits, and the required number of SAIlocation circuits; calculating a total power delivered over the linepower system; calculating a CO location circuit availability measure andan SAI circuit availability measure based on the line length, the numberof CO location circuits, the number of SAI location circuits, therequired number of line power system circuits, the total powerdelivered, and a plurality of parameters representing SAI locations,environmental variables, and/or failure or repair statistics associatedwith the line power system; and calculating a line power systemavailability measure based on the loop length, the number of CO locationcircuits, the number of SAI location circuits, the required number ofline power system circuits, the total power delivered, and a pluralityof parameters representing serving area interface locations or repairtime statistics associated with the line power system.
 14. The method ofclaim 13 further comprising: comparing the line power systemavailability measure with a predetermined availability metric;determining a new number of CO location circuits required in the linepower system, or a new number of SAI location circuits required for theline power system, a new number of lines per circuits, if the line powersystem availability measure is less than the predetermined availabilitymetric.
 15. The method of claim 14 further comprising recalculating theline power system availability measure based on the new number of COlocation circuits, a new number of SAI location circuits required forthe line power system, or a new number of lines per circuits.
 16. Themethod of claim 13 where determining a loop length, determining a numberof CO location circuits, and determining a number of SAI locationcircuits comprises accessing a database of one or more parametersassociated with the loop length, CO location circuits, and SAI locationcircuits.
 17. The method of claim 13 where the repair time statisticscomprise a mean-time-to-repair distribution associated with the powercircuit units.
 18. The method of claim 13 where the environmentalvariables comprise ambient temperature, ambient humidity, windvelocities, solar exposure factors, latitude, and ground albedo.
 19. Themethod of claim 16 where the database comprises a database selected fromthe group consisting of: an Automated Records and Engineering System(ARES), Loop Facilities Assignment and Control System (LFACS), or LoopEngineering Information System (LEIS) database.
 20. The method of claim13 where calculating a required number of line power system circuits andcalculating a total power delivered comprise utilizing a powercalculator.
 21. The method of claim 13 where the line power systemcomprises a very high bit rate digital subscriber line (VDSL) system orasymmetric digital subscriber line (ADSL) system.
 22. The method ofclaim 13 where the power circuits further comprise a CO DC-DC powerconverter, an SAI DC-DC power converter, and a plurality of twisted pairpower lines interconnecting the CO power converter and the SAI powerconverter.
 23. The method of claim 13 where the failure statisticscomprise failure-in-time rates (FITS) of the CO DC-DC converters, thepower lines, and the SAI DC-DC converters.
 24. The method of claim 13where the power circuits comprise feeder circuits connecting the centraloffice (CO) and the serving area interface (SAI).
 25. The method ofclaim 24 where the feeder circuits comprise one or more copper linepairs.
 26. A computer program product for calculating availability for aline power system, the line power system comprising at least three powercircuits further comprising: a computer useable medium having computerreadable code embodied in the medium, the computer readable codecomprising: computer readable code executable to determine a pluralityof power circuit parameters characterizing each of the power circuits;computer readable code executable to calculate a required number ofpower circuits in the line power system; computer readable codeexecutable to calculate a total power to be delivered over the linepower system; computer readable code executable to calculate a firstpower circuit availability measure and a second power circuitavailability measure based on the power circuit parameters and aplurality of external variables; and computer readable code executableto calculate a line power system availability based on the first powercircuit availability, the second power circuit availability, and theplurality of external variables.
 27. A computer program product forcalculating availability for a line power system, the line power systemcomprising at least one power circuit unit interconnecting a centraloffice (CO) location and a serving area interface (SAI) location,further comprising: a computer useable medium having computer readablecode embodied in the medium, the computer readable code comprising:computer readable code executable to determine a loop length requiredfor the line power system; computer readable code executable todetermine a number of CO location circuits required in the line powersystem; computer readable code executable to determine a number of SAIlocation circuits required for the line power system; computer readablecode executable to calculate a required number of line power systemcircuits based on the required loop length, the required number of COlocation circuits, and the required number of SAI location circuits;computer readable code executable to calculate a total power to bedelivered over the line power system; computer readable code executableto calculate a CO location circuit availability measure and an SAIcircuit availability measure based on the loop length, the number of COlocation circuits, the number of SAI location circuits, the requirednumber of line power system circuits, the total power delivered, and aplurality of parameters representing serving area interface locations,environmental variables, and/or failure or rep statistics associatedwith the line power system; and computer readable code executable tocalculate a line power system availability measure based on the looplength, the number of CO location circuits, the number of SAI locationcircuits, the required number of line power system circuits, the totalpower delivered on a plurality of parameters representing serving areainterface locations or repair statistics associated with the line powersystem.